[1]} suggest that this HMXB originates from the OB association of Sco OB1, of which NGC 6231 is the core. This is based on astrometric data from Hipparcos, and more recent data from Gaia DR2 corroborates this finding [2]}. The companion star in 4U 1700-377 is an early supergiant (O6 Ia, [3]} [3]}) weighing 46\(\pm \) 5 M\(_{\odot }\)  [5]}. This implies that the compact object formed no more than a couple million years ago, otherwise the companion star would have evolved into a compact object as well.
